A variable displacement engine includes engine cylinders that may be deactivated from time to time to conserve fuel. By deactivating a fraction of the engine's cylinders, activated cylinders may be operated at a higher efficiency. Pistons of deactivated cylinders may reciprocate within the deactivated cylinders while intake and exhaust valves of the cylinders are held closed. The deactivated cylinders may hold fresh air or exhaust to reduce vacuum within the cylinders, but engine power may be lost by compressing and expanding the air. The compression and expansion of the air provides minimal useful work. Therefore, it would be desirable to increase the amount of useful work provided by one or more deactivated cylinders.
The inventor herein has recognized the above-mentioned issues and has developed an engine control method, comprising: deactivating a cylinder of an engine via a controller ceasing to supply fuel to the cylinder, the engine a four stroke engine; and drawing air into the deactivated cylinder from a vacuum reservoir during a first stroke of four strokes in a cycle of the deactivated cylinder, the air drawn into the deactivated cylinder without having passed through a passage of an intake manifold that leads to other cylinders of the engine.
By adjusting valve timing of a deactivated cylinder, the deactivated cylinder may be utilized in a way that may increase engine efficiency while the cylinder is deactivated. Specifically, a second intake valve may be opened to provide vacuum to a vacuum reservoir during an intake stroke of the deactivated cylinder. The air inducted to the cylinder may then be ejected to the engine's intake manifold to increase intake manifold pressure and feed other engine cylinders with air. The exhaust valves of the deactivated cylinder may be opened during a power stroke of the deactivated cylinder to draw exhaust gas into the deactivated cylinder. The first intake valve may be opened during an exhaust stroke of the cylinder to recirculate exhaust gas to other engine cylinders.
The present description may provide several advantages. In particular, the approach may improve engine efficiency when an engine operates with one or more deactivated cylinders. Additionally, the approach may provide vacuum when vacuum production may be difficult. Further, the approach may provide higher exhaust gas recirculation (EGR) flow rates during conditions when intake manifold pressure may be higher.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.